Storyline courses not loading after computer upgrade

Hi there,

I recently changed over to a new iMac from an old Mac tower. On my old system, Storyline courses worked perfectly in my browser. On the new system, the Flash versions of the courses do not load, instead the page stays blank and I get a 'Movie not loaded' message when I right-click on the blank screen area. The HTML5 version of the course loads fine, and Flash videos load fine on other sites.

I've doubled checked that both my OS (OSX 10.10.5) and Flash (18,0,0,232) are up-to-date, and even tried uninstalling and re-installing Flash.

Is there some type of incompatibility with Storyline Flash exports and the newest Mac OS?

EDIT: I've tried to open the files in Firefox, Chrome, and Safari on my Mac side, and in Firefox and IE on my Windows partition via Parallels with no luck. The files are hosted on an FTP for preview purposes which we've been using for years without issue.